feat(next): provide request context in lazy initialization for RSCs

- add createRequestFromHeaders utility for consistent request creation
- pass constructed Request to config function instead of undefined
- enable request-based config customization for RSCs, matching other contexts
- support documented use cases like env-specific provider configuration
- allow header/request access during server-side auth() calls

packages/next-auth/src/index.ts

@@ -46,7 +46,7 @@
  * If you need to override the default values for a provider, you can still call it as a function `GitHub({...})` as before.
  *
  * ## Lazy initialization
- * You can also initialize NextAuth.js lazily (previously known as advanced intialization), which allows you to access the request context in the configuration in some cases, like Route Handlers, Middleware, API Routes or `getServerSideProps`.
+ * You can also initialize NextAuth.js lazily (previously known as advanced intialization), which allows you to access the request context in the configuration in some cases, like Route Handlers, React Server Components, Middleware, API Routes or `getServerSideProps`.
  * The above example becomes:
  *
  * ```ts title="auth.ts"

packages/next-auth/src/lib/index.ts

@@ -117,6 +117,19 @@ function isReqWrapper(arg: any): arg is NextAuthMiddleware | AppRouteHandlerFn {
   return typeof arg === "function"
 }
 
+/**
+ * Creates a Request object from Headers, primarily for server-side contexts
+ * where we need to reconstruct request information.
+ */
+function createRequestFromHeaders(headers: Headers): Request {
+  const url = headers.get("x-url") ||
+    `${headers.get("x-forwarded-proto") || "http"}://${headers.get("host")}`;
+
+  return new Request(url, {
+    headers: new Headers(headers)
+  })
+}
+
 export function initAuth(
   config:
     | NextAuthConfig
@@ -128,10 +141,11 @@ export function initAuth(
       if (!args.length) {
         // React Server Components
         const _headers = await headers()
-        const _config = await config(undefined) // Review: Should we pass headers() here instead?
+        const _request = createRequestFromHeaders(_headers)
+        const _config = await config(_request)
         onLazyLoad?.(_config)
 
-        return getSession(_headers, _config).then((r) => r.json())
+        return getSession(_request.headers, _config).then((r) => r.json())
       }
 
       if (args[0] instanceof Request) {
@@ -183,9 +197,10 @@ export function initAuth(
   return (...args: WithAuthArgs) => {
     if (!args.length) {
       // React Server Components
-      return Promise.resolve(headers()).then((h: Headers) =>
-        getSession(h, config).then((r) => r.json())
-      )
+      return Promise.resolve(headers()).then((h: Headers) =>{
+        const request = createRequestFromHeaders(h)
+        return getSession(request.headers, config).then((r) => r.json())
+      })
     }
     if (args[0] instanceof Request) {
       // middleware.ts inline